1. Field of the Invention
The present invention relates to a wiring pattern inspection apparatus in which a defective in a wiring pattern formed on a printed wiring board, a photomask or the like is inspected.
2. Description of the Prior Art
The inspection to find out a defective in a printed wiring board has conventionally relied on a visual inspection performed by a human. However, as products are miniaturized and lightened, a wiring pattern formed on the printed wiring board is miniaturized and complicated more and more. Therefore, it is difficult to inspect the miniaturized wiring pattern with a high inspecting precision. Also, it is difficult to inspect the miniaturized wiring pattern for a long time. As a result, the automatization of the inspection has been strongly required.
As a conventional example of a visual inspection apparatus for inspecting a printed wiring board, various types of inspection apparatuses are proposed in a literature (Y. Nakagawa, and T. Ninomiya: "A Visual Inspecting Technique of Electronic Circuit Boards", O plus E, No.132, pp.138-152 (November 1990)). Pattern inspecting method are roughly classified into a characteristic extracting method (or a design rule checking method) and a comparison inspecting method. In the design rule checking method, it is Judged whether or not a wiring pattern departs from a design rule by inspecting characteristics of a line width and the wiring pattern such as a connecting point, an ending point and the like. For example, the design rule checking method has been proposed in the Japanese Published Unexamined Patent Application No. 15343 of 1986 and in the Japanese Published Unexamined Patent Application No. 263404 of 1987.
Also, in the comparison inspecting method, an inspected pattern displayed in an image plane is compared with a reference pattern of a good product or a design pattern for each of pixels. For example, the comparison inspecting method has been proposed in the Japanese Published Unexamined Patent Application No. 61604 of 1985 and in the Japanese Published Unexamined Patent Application No. 140009 of 1987.
3. Problems to be solved by the Invention
However, each of the above methods has both merits and demerits, so that various methods have been proposed to compensate the above methods for the demerits. For example, in the literature (Y. Nakagawa, and T. Ninomiya: "A Visual Inspecting Technique of Electronic Circuit Boards", O plus E, No.132, pp.138-152 (November 1990)), the characteristic extracting method and the comparison inspecting method are combined to adopt the merits of the characteristic extracting method and the comparison inspecting method for the purpose of compensating for the demerits. Also, a hopeful method has been proposed in the Japanese Published Unexamined Patent Application No. 180404 of 1989. In this application, a plurality of inspecting methods are prepared in advance to apply one of the inspecting methods for each of pattern regions to be inspected, and a group of pattern regions which are inspected according to a prescribed inspecting method is determined. This determination is performed for each of the inspecting methods. To be concrete, either the characteristic extracting method or the comparison inspecting method is selected for each of the pattern regions.
However, because a wiring pattern is miniaturized and complicated in recent years, there is a drawback that it is difficult to manually set one of the inspecting methods for each of a plurality of pattern regions in the range of several tens to several hundreds in number. Also, there is another drawback that a position of a wiring region for which one of the inspecting methods is set does not accord with that of a printed wiring board to be inspected.